America's population size, economic strength and industrial powers allowed the US to not only build up her armies, but also supply allies through the lend-lease act. In fact, with all the population & natural resources the US owned, they were able to build almost as fast as their equipment being destroyed, hence a quote of "Once a .. .[tank in this instance] was destroyed, it was pushed out of the way, and replaced at once..."
Answer: The 10th amendment explains that the powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.
